The present invention relates in general to a control apparatus for controlling movements of an electrode in an electric arc furnace, wherein a hydraulic cylinder is provided to adjust the electrode, the operating chamber of said cylinder being connected to a pressure source or to reservoir via a valve which is actuated by a control signal which is produced in comparing the actual value and a desired value of the electric arc current.
It is known in the art of adjusting an electrode of an electric arc furnace to maintain the electrical current of the arc as constant as possible by either manually or automatically adjusting the current depending on requirements of operation. The control signal produced in a comparison circuit to which the actual value and the desired value of the electrical current are fed controls a servo valve which connects the hydraulical cylinder either to a pressure source or to reservoir to thus raise or lower the electrode to keep the current constant.
The electric arc can be ignited only after the electrode touches upon conductive material to be melted. As the operating chamber of the cylinder is connected to the reservoir for lowering the electrode, fluid is displaced out from the operating chamber to the reservoir via the valve in the moment of touch-down of the electrode. It is apparent that the electrode is thus not hydraulically supported. This is a substantial drawback since the electrode may sink down in an uncontrolled movement. This results in the danger of overcurrent, short-circuit or breakage of the electrode.